1. Field of the Invention
The present invention relates to power jack electrical connectors, and more particularly to direct-current power jacks susceptible to in-rush current sparking when mating with a complementary power plug.
2. Description of the Related Art
A typical direct-current (DC) power jack includes a central contact and spring contacts for electrically engaging with a direct-current power plug. A conventional DC power jack, such as that disclosed in U.S. Pat. No. 5,927,999, has three movable spring contacts around the central contact. When mating with a power plug, the three spring contacts simultaneously engage with a corresponding terminal of the plug. Such multi-point contacting allows a larger current to flow from the plug to the jack.
Another conventional DC power jack, such as that disclosed in U.S. Pat. No. 5,007,851, includes a central contact, a fixed tab contact and a movable spring contact. The tab contact and the spring contact function as a switch so that a circuit can detect whether the jack has properly engaged with a power plug. When the jack is not engaged with a plug, the spring contact contacts the tab contact. When the plug is inserted into the jack, the spring contact separates from the tab contact.
In the above two conventional power jacks, electrical connection between the plug and the jack is established immediately upon the contacts thereof engaging together. There is frequently a high voltage difference between the contact of the plug and the contact of the jack. Instantaneous electrical connection therefore often causes an in-rush current spark to jump from the contact of the plug to the contact of the jack. Such sparking degrades the contacting characteristics of the contacts, and increases the resistance of the contacts. Furthermore, repeated sparking can eventually result in malfunction of both the jack and the plug. Accordingly, a DC power jack that eliminates in-rush current sparking is desired.
In view of the foregoing, a main object of the present invention is to provide a direct-current (DC) power jack which prevents in-rush current sparking when the power jack engages with a power plug.
To achieve the above-mentioned object, a DC power jack in accordance with the present invention includes an insulative housing and a hole defined in a front face of the housing for insertion of a complementary power plug thereinto. The power jack also includes a ground contact, a center contact, first and second switch contacts, first and second conductive contacts and a joining member. When the plug is inserted into the power jack, it electrically connects firstly with the ground contact. The plug then electrically connects with the center contact. The plug then pushes the first switch contact to cause the first conductive contact to electrically connect with the joining member, and then pushes the second switch contact to cause the second conductive contact to electrically connect with the joining member.
An electrical circuit electrically connected with the power jack includes a ground circuit, a resistor, a capacitor and a load. The ground circuit connects with the ground contact. When the plug electrically connects with the center contact, power from the plug flows through the center contact and the resistor to charge the capacitor. When the first conductive contact connects with the joining member, power from the plug flows through the center contact, the joining member and the first conductive contact to charge the capacitor. When the second conductive contact connects with the joining member, power accumulated in the capacitor flows through the resistor and the second conductive contact to the load.